Patent GB-1126966-A (GB)
Title: Improvements in or relating to superconducting magnets
Inventor: WILLIAMS MICHAEL
IPC: H01L39/14
Filed: 1965-12-10
Abstract: 1,126,966. Superconductor magnets. GENERAL ELECTRIC CO. Ltd. 8 Feb., 1967 [10 Dec., 1965], No. 52565/65. Headings H1K and H1P. A superconductor device is produced by forming a sintered body of superconductor material in the form of a hollow cylinder the ends of which are bridged by at least one loop and cutting a helical slot in the wall of the cylinder to form a solenoid the ends of which are bridged by each of the loops. The device is produced by pressing and sintering a mixture of niobium and tin powders to form a rectangular plate with a solid circular cylinder extending along one edge. A pilot hole (34) is bored through the cylinder and a rectangular slot (12) is cut in the plate adjacent to the cylinder by spark erosion, Fig. 2 (not shown). The ends of the pilot hole are plugged and the body is electroplated with copper, the plugs are removed and the ends of the cylinder and plate, and that edge of the plate remote from the cylinder are machined to remove the copper layer. The bore in the cylinder is enlarged and a thread 38 is tapped in it. The thread is then deepened by means of a second tap so that it extends completely through the thickness of the niobium-tin cylinder to form a solenoid, the copper layer serving to support the turns, and a rectangular slot 13 is cut in the remainder of the plate by spark erosion, Fig. 4. Heating coils are wound round bridges 10 and 11 from which they are electrically insulated. The copper layer physically supports the solenoid and loops and also in use provides a low resistivity shunt path in the event of any localized part of the body turning normal. The end turns of the solenoid may be of reduced pitch produced by cutting the thread by spark erosion using a rotating electrode in the bore, the body being traversed at suitable rates. The device may be magnetized by placing the core of an electromagnet through outer slot 13, cooling the device to the superconducting state, energizing a first coil (17) to make arm 11 normal, energizing the electromagnet, deenergizing the first coil (17) to allow arm 11 to return to the superconducting state, slowly deenergizing the electromagnet to generate a circulating current, energizing a second coil (14) to transfer part of the trapped flux to loop 12 and the solenoid, de-energizing the second coil (14), and repeating the process several times to build-up the field, Fig. 1 (not shown). In an alternative method, Figs. 5 and 6 (not shown), a magnetic core is passed through the outer slot (13) and a rotating horseshoe type permanent magnet is provided so that when its poles are adjacent to the core a flux threads the slot (13). As the poles of the magnet move towards the core, the first coil (17) is energized until the magnetic flux in the slot (13) is a maximum. The magnet continues to rotate and when its poles are furthest from the core the second coil (14) is energized and then de-energized to transfer part of the flux trapped in the outer slot (13) to the solenoid, the first coil (17) is re-energized and the process is repeated several times to build up the required field. In a second embodiment, Fig. 7, only a single loop is provided and the part 21 lying parallel to the solenoid comprises a thin layer of soft superconductor material. This may be produced by using niobium powder for part of the plate when moulding the basic body or by bridging two arms of powdered niobium-tin with a thin foil of niobium and then sintering. The strip 21 is so thin that the flux of a permanent bar magnet 22 can penetrate it over a region, e.g. 24, smaller than the width of the strip 21. The solenoid is magnetized by moving the bar magnet in a loop across, and close to, the strip 21 and then across, but a large distance from, one of the side arms 9. This enables the flux due to the magnet to be threaded through the loop where it is maintained when the magnet is removed across the side arm. The required field can be built up by repeating the movement of the magnet. The penetration of the magnetic flux through the strip 21 may be aided by a radiation spot (not shown). The initial material may be powdered superconductor material rather than a mixture of its ingredients.